The present invention pertains to a polyvinylidene fluoride (PVDF) product at least one of whose surfaces is coated with fine particles of PVDF. The present invention also pertains to the process for treating a PVDF surface consisting of coating it with PVDF particles to facilitate the subsequent adhesion of a polymer incompatible with the PVDF to the said surface. The process consists of attaching PVDF particles to the PVDF surface.
PVDF has been known for its resistance to chemical agents and its resistance to atmospheric factors. These properties have made it a material that is particularly suitable as a protective coating for materials that are characterized by good mechanical strength but are susceptible to chemical or atmospheric corrosion. For example, the use of PVDF as a protective layer for thermosetting resins has developed in the manufacture of corrosion resistant components (tanks, vessels, piping systems).
In contrast, the anti-adhesive properties of PVDF makes it use complicated. Means have been developed during the past few years to make possible its adhesion to other bodies, particularly to synthetic resins, directly in the form of finishing layers or in the form of adhesive primers. The synthetic adhesive primer issued, in particular, as an intermediate for coating metal parts with PVDF.
It was proposed in French Patent No. 2,346,426 that a fibrous substrate should be applied to the PVDF surface by means of a PVDF solution in an aprotic polar solvent to render a PVDF surface adhesive for any surface.
It was proposed in U.S. Pat. No. 3,723,234 and DE-OS No. 2,818,385 that the PVDF surface should be impregnated, in the hot state and under pressure, with fibers or fabric to create an adhesive surface for other polymers.
These industrially utilized processes have the disadvantage of associating with the final PVDF-polymer composite a foreign intermediate in the form of fibers or fabric, which is not always advantageous. For example, when these composites are used, it is necessary to remove the fibrous substrate over a certain width along the welding or fusion lines prior to any welding or fusing operation. One of the disadvantages of this operation is that nonadhesive zones or at least zones in which separation and corrosion will begin are created along the welding or fusion lines.
Another known method consists of adhering particles of an inorganic substance, such as alumina or silica, to the PVDF from a solution of PVDF in a solvent. A foreign intermediate that is unfavorable as before is thus again interposed between the PVDF and the substrate to be adhered, particularly at the junctions.